1. Field of the Invention
The invention relates to the manufacture of tetrahydrofurans which are useful as solvents and polymer intermediates. In particular, the invention relates to the manufacture of tetrahydrofurans from corresponding gamma-chloroalkanols.
2. Prior Art
Tetrahydrofurans and particularly tetrahydrofuran (THF) itself are important products of commerce which find their principal utility as solvents and polymer intermediates. Of the many tetrahydrofurans, by far the most important commercially is THF which finds countless applications because of its excellent solvent properties. For example, THF is an excellent solvent for high molecular weight polyvinyl chloride resins and vinylidene chloride polymer used for top coating vinyl fabric and sheeting, coating cellophane, protective coatings, vinyl adhesives, printing inks and film coating. It is also used as solvent or reaction medium for synthetic polymers, natural resins, organometallic compounds, for Grignard reactions, hydride reductions, stereospecific polymerizations, condensations and esterifications. In addition, THF is useful as an intermediate for synthesis of pyrrolidine, tetrahydrothiophene and as a monomer or comonomer for certain polymerization reactions.
Commercially, THF is usually made by one of the following three routes using the indicated basic starting materials.
__________________________________________________________________________ A. Acetylene/Formaldehyde ##STR1## ##STR2## ##STR3## B. Furfural ##STR4## ##STR5## C. Butadiene/Chlorine ##STR6## ##STR7## ##STR8## ##STR9## __________________________________________________________________________
Though all three of the above-described processes are in commercial use, they nevertheless have certain disadvantages. For example, all three processes include an hydrogenation step which is quite high in its initial capital cost and, furthermore, requires extensive facilities for providing large amounts of hydrogen. In addition, processes based on acetylene are becoming more costly because of energy factors and the extraction of furfural from corn cobs or oat hulls is also quite expensive. Thus, there is clearly a need for alternative processes utilizing different starting materials to produce THF and other tetrahydorfurans in high yields and/or selectivity.
The cyclization of chlorobutanols to tetrahydrofuran is known in the prior art. The usual procedure is to treat the chlorobutanol with aqueous or alcoholic base (C. Walling and A. Padwa, J. Am. Chem. Soc., 83 2208 (1961); E. L. Jenner, J. Org. Chem., 27 1032 (1962); C. Walling and J. Bristol, J. Org. Chem., 37 3515 (1972). The thermal conversion of chlorobutanol does produce some tetrahydrofuran in addition to high boiling products. A partial conversion of tetramethylene chlorohydrin to THF in a system containing 1,4-dichlorobutane is reported in U.S. Pat. No. 2,950,232.
Until recently it was not considered synthetically possible to selectively chlorinate alkanols to chloroalkanols. Huyser (Methods in Free Radical Chemistry, Vol I, Marcel Kebber, N.Y. 1969) pointed out that photochlorination of alkanols was not a useful route to chloroalkanols because the reaction proceeds rapidly to oxidation with the formation of carbonyl compounds and chlorinated carbonyl compounds. However, Kollonitsch et al. (J. Chem. Soc. 1093 (1967)) showed that chlorination of butanol in liquid HF provided a mixture of 4-, 3- and 2-chlorobutanols with the 3-chloro-compound as the main product. Some improvement in the selectivity of chlorination of butanol was recently shown by Deno et al. (J. Org. Chem., Vol. 39 No. 4, P520 (1974)) using an aqueous acetate buffer system. However, no prior art is known for the selective chlorination of n-butanol to more than 50% 4-chloro-1-butanol.